Soldering iron tips

[Domagoj T]

If I type into the google "soldering iron tips" I get 15+ million results on how to select the proper tips for you iron, or how to clean it, or different brands etc, but what I was not able to find are tips on how to solder iron.

I have several different fluxes available and all but two fail miserably. One of the two fluxes that works is an oily liquid that soils the soldering iron to such an extent that after a single joint I decided that I will never use a soldering iron with that flux again. The other flux that works is a powder for silver soldering or brazing and basically requires the metals to get red hot to activate the flux, which means a butane torch is needed. Unfortunately that is too hot for my needs.

I am looking for a flux that can work at lower temperatures, preferably with standard electronics leaded solder and will help make a decent bond on iron based alloys, specifically model train tracks. Usually soldering to rail joners is fine and works, but Marklin K track is resisting everything I've tried (except the two above mentioned). The temperature should be relatively low so as not to melt the ties/sleepers.

Any suggestions?

[garethw]

I use Loctite Rosin core solder and a "No Clean" flux pen for larger jobs.
It may be that the track is conducting the heat away too quickly and preventing the solder from joining.

Gareth

[Ian.M]

Getting most solder alloys to wet an iron or steel surface without aggressive flux is difficult. However you cant use acid fluxes, high halides fluxes, etc. because its impossible to clean them 100% from the stranded wire you are attempting to solder to the track, and their residue will corrode the strands up under the insulation and cause rapid failure of the wire.   You can pre-tin with an aggressive flux, then thoroughly clean  the tinned area and surroundings (and if the cleaning isn't a multi-step process with solvents and then very hot water, it probably isn't thorough enough), then solder the wire to the tinned area using ordinary solder with non-aggressive flux.

Alternatively, try applying a drop of strong Copper Sulphate solution to the freshly cleaned iron or steel to 'flash' plate it with an easily solderable copper layer.  After a minute or two wipe off with a tissue or disposable wipe, wipe again with a damp tissue or wipe to rinse the surface, dry. and immediately flux with an ordinary rosin based flux and solder.

[Domagoj T]

Copper Sulphate

Thanks, I have some. I'll try it and report back.

[zomehi]

Hi,

If you can live with weak mechanical strength and very very high price then you could look into ultra sonic soldering stations. These are used to solder tinned copper ribbons on steel substrates in photovoltaic industry. The soldering temperature can low as 150C with these stations.

Another solution could be to use pure indium instead of Sn based solder.

[KL27x]

The "soiling" of the iron tip is part and parcel of the high temps you need in the small iron tip in order to heat up relatively large pieces of steel. Just wipe off the burnt flux residue on a sponge or piece of brass wool and carry on.

You could try flux designed for lead free. In some cases it will be formulated for higher temps, the way that brazing flux melts at much higher temps.

I think the white powder flux for brazing is anhydrous boric acid. The salt form of folic acid is folate. I dunno why not "borate?" But, yeah, that would sound kinda dumb.

[Ian.M]

The O.P's trying to solder to HO gage model rail.  Due to steel's lower thermal conductivity than copper, it shouldn't be a problem with eccessive flux burning while getting the joint up to soldering temperature, as any decent temperature controlled iron should be able to solder to solid copper wire of similar cross sectional area, reasonably quickly if a suitable large hoof bit is used.   OTOH if he's using an underpowered iron with a poncy little long conical bit, you could well be on to something.

[KL27x]

copper wire of similar cross sectional area

I am assuming the tracks are relatively thick for w/e tip he is using. And there is thermal mass to consider in addition to heatsinking. I use regular rosin flux to solder steel a few times. Works fine. And my soldering iron is constantly "soiled" with black residue even when soldering tiny SMD parts.

[Domagoj T]

I don't think ultrasonic equipment would be justified, but thanks, the technology looks interesting.
The crud on the soldering iron from that specific flux was not your everyday crud. I spent about half an hour getting it off my tip using brass wool and it was never the same again.
Unfortunately I don't have any lead free stuff on hand. I might look into getting some.
Yeah, brazing stuff is based on boric acid, but it's got something else in it too. In any case, activation temperature for this particular flux is way too high for this application.
The crossection of track is comparable to some thicker wires, thermal mass should not be the issue. I've soldered thicker copper wires without much problem.
I have the Weller PU 81 station and WSP 80 iron. It's 80W, so should be good enough. The tip is a 2,5mm chisel.

All in all, yesterday, I tried with Copper Sulphate, but had no luck. Decide to give it another go and leave the crystals to dissolve overnight. Today, I left a drop of it on the rail for some 20 minutes (I got distracted by other stuff) and after that the solder made a good bond (stronger than a 0,14mm^2 copper wire, which is good enough for me).

Thank you, Ian (and the rest of you guys)!

[zomehi]

I don't think ultrasonic equipment would be justified, but thanks, the technology looks interesting.
The crud on the soldering iron from that specific flux was not your everyday crud. I spent about half an hour getting it off my tip using brass wool and it was never the same again.
Unfortunately I don't have any lead free stuff on hand. I might look into getting some.
Yeah, brazing stuff is based on boric acid, but it's got something else in it too. In any case, activation temperature for this particular flux is way too high for this application.
The crossection of track is comparable to some thicker wires, thermal mass should not be the issue. I've soldered thicker copper wires without much problem.
I have the Weller PU 81 station and WSP 80 iron. It's 80W, so should be good enough. The tip is a 2,5mm chisel.

All in all, yesterday, I tried with Copper Sulphate, but had no luck. Decide to give it another go and leave the crystals to dissolve overnight. Today, I left a drop of it on the rail for some 20 minutes (I got distracted by other stuff) and after that the solder made a good bond (stronger than a 0,14mm^2 copper wire, which is good enough for me).

Thank you, Ian (and the rest of you guys)!

Great. Might try copper sulphate someday.